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  1. #1
    Join Date
    Jul 2008
    Location
    Huntsville AL
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    4

    Filter Size and Pressure Drop Question

    Just got a new Trane Package Heat Pump. I had read a discussion of air filters here a few weeks ago, and requested a 4 inch media filter. The contractor at first said I needed a bigger filter grill because my present one is 20 x 25. Once he saw that he'd have to cut into wall joists his story changed to me not needing a bigger size. Manual says 4 sq feet with a w.c. between .05 and .08 (it was contradictory) at a 300 fpm flow rate. I checked and the honeywell 4 inch Merv 10 filter has a w.c. of .21. So I'm in a pickle. Even with a bigger grill (which I'll have to demand), I'm way over the recommended w.c. rating for my unit. I don't see how any efficient filter is going to meet spec. Any advice?

    Thanks,

    Jim

  2. #2
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
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    3,304
    Quote Originally Posted by eldrijt View Post
    Just got a new Trane Package Heat Pump. I had read a discussion of air filters here a few weeks ago, and requested a 4 inch media filter. The contractor at first said I needed a bigger filter grill because my present one is 20 x 25. Once he saw that he'd have to cut into wall joists his story changed to me not needing a bigger size. Manual says 4 sq feet with a w.c. between .05 and .08 (it was contradictory) at a 300 fpm flow rate. I checked and the honeywell 4 inch Merv 10 filter has a w.c. of .21. So I'm in a pickle. Even with a bigger grill (which I'll have to demand), I'm way over the recommended w.c. rating for my unit. I don't see how any efficient filter is going to meet spec. Any advice?

    Thanks,

    Jim
    I believe it would be useful info to know the CFM you plan to flow through the filter. As a fellow homeowner, I would ask if there would be any opportunity to add a 2nd return as an alternative to enlarging the original one. That is what I had done. There's a lot of things I don't know but one thing I have learned is: the pressure drop goes way down based on the feet/min air speed at filter face going down, which in turn is dictated by your CFM airflow.

    Even 0.21 might be within the specified capabilites of your air handler. My Trane mfg VS (variable speed) air handler is spec'ed to deliver nearly constant airflow up to 0.90 total ESP, it just would use some extra electricity to do that.

    Best of luck -- Pstu

  3. #3
    Join Date
    Apr 2008
    Location
    Princeton, NJ
    Posts
    581
    I have a Trane XV95/XL15i 100Kbtu/4-ton system with a reccomendation of a 20x25 filter (Eventhough my side-return installation is only sized for a 17x25 max). Go figure

    Anyway, I had a new return drop installed with a cabinet that can handle 20x25 filters from 1 to 5 inch (primarily due to the horizontal installation).

    In an effort to get my static pressure down, several low cost filters were tested for pressure drop and here is the data.

    The blower is set on 400CFM/ton (1600 CFM) but is likely delivering only 1400 CFM at my static high pressure according to the servicts facts section in the installation manual.

    1. The blue cheapo see-thru filter was 1 inch thick and had a pressure drop of 0.05.
    2. The 5" Merv-10 media filter that came with the GeneralAire cabinet had a PD of 0.14.
    3. The 1" Merv-7 pleated filter (Ace Hardware brand) that looked identical to a Merve-8 Natralaire pleated filter, had a very high PD of 0.27
    4. A 1" thick Merv-4 Naturalaire washable Fiber filter had a PD of 0.07 .

    I decided to stay with the merv-4 since it it is better than the basic blue cheapo filter and a rating of merv-4 is not to bad if no smokers or pets in the house. In pollen season I will likely switch to the 5" GeneralAire Merv 10 filter.

    Key1

  4. #4
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by pstu View Post
    I believe it would be useful info to know the CFM you plan to flow through the filter. As a fellow homeowner, I would ask if there would be any opportunity to add a 2nd return as an alternative to enlarging the original one. That is what I had done. There's a lot of things I don't know but one thing I have learned is: the pressure drop goes way down based on the feet/min air speed at filter face going down, which in turn is dictated by your CFM airflow.

    Even 0.21 might be within the specified capabilites of your air handler. My Trane mfg VS (variable speed) air handler is spec'ed to deliver nearly constant airflow up to 0.90 total ESP, it just would use some extra electricity to do that.

    Best of luck -- Pstu
    Ditto!

    Tell us more abot the system,tons,model numbers,pics,etc..

  5. #5
    Join Date
    Apr 2008
    Location
    Princeton, NJ
    Posts
    581
    oh...all data was generated at the 100% blower speed (not the 80%).
    Key1

  6. #6
    Join Date
    Jul 2008
    Location
    Huntsville AL
    Posts
    4
    My Trane is a 3 ton package unit heat pump, XL16C, 16 Seer, 2 stage

    Extra return would be a major pain in my house. Good info on the P drops of diff filters. Was really hoping to attack the allergies with a high efficiency filter.

    Thanks,

    Jim

  7. #7
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    What the static pressure,supply and return??

    Duct system will need rework if static is too high,this can usually be done,space available,chage out high static elbows,fittings ,etc..

  8. #8
    Join Date
    Apr 2008
    Location
    Princeton, NJ
    Posts
    581
    Quote Originally Posted by eldrijt View Post
    Good info on the P drops of diff filters. Was really hoping to attack the allergies with a high efficiency filter.

    Thanks,

    Jim
    That should not be a problem if the static pressure is not too high.....and if it is too high there are ways to address it....

    Key1

  9. #9
    Join Date
    Jul 2008
    Location
    Huntsville AL
    Posts
    4
    The guy came by today and agreed to put in a 20 x 30 Grill. That gives me a little (4%) more area than the 2 sq ft Trane recommends. And 20% more than I had with the 20x25. The 20 x 30 filter is here http://customer.honeywell.com/honeyw...aspx/FC40R1029 which shows .12 w.c. at 300 cfm. I'm not at the .08 (at 300 cfm)Trane recommends but I'm guessing that's close enough. The rest of my system ducts are straight shots from my unit to return and back, so I don't have any other unusual restrictions. Yes a bunch of measurements would be best. I've got a 10 yr full warranty so that makes me feel OK with going fwd. Since this grill is a standard grill, I can switch to any other 20 x 30 in the future. Filtrete etc, if I decide the Honeywell is too restrictive.

    Thanks everybody!

    Jim

  10. #10
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
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    Guesing the filter is 19X29,1200 cfms ,you are about 350 fpm,so a little more PD.

    It that okay,really depends on those tests, etc.,could be an issue,I'd have the static tested.If they can't do it,well find another.
    Last edited by dash; 08-01-2008 at 03:16 PM.

  11. #11
    Join Date
    Jul 2008
    Location
    Huntsville AL
    Posts
    4
    Thanks Dash. I'll ask him to measure. If measurements show a problem, I guess at that point all I could (easily) do would be use a less restrictive filter. Adding another return would take up closet space we don't have to spare. Maybe I could use a electronic filter like an Aprilaire 5000. I'll have to look at how restrictive that is also. Another thing I've contemplated is how restrictive is the Trane Clean Effects?! If it's more restrictive then why should I worry? I'll look into that too.

    Jim

  12. #12
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    18,836
    The filter is just one part of the system static,there are many things that can be done to reduce the system static,other than filter type and size.

    Turning vanes in elbows,larger ducts ,parallel trunks,low PD fittings,,etc.,etc.

    So if you want better filtration,look into changes that can keep the static low enough to deliver the minimum required cfms.

  13. #13
    Join Date
    Feb 2008
    Location
    Dallas & Longview, TX
    Posts
    629
    Usually package units have short return runs to the outside unit. The total filter area is more important than the ducting getting it to the filter so adding a 4" filter at the unit and at the size you require would eliminate increasing the size of the actual duct getting it to the filter in many cases. What size is the return duct?

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